The present invention relates to a flame-retardant resin composition. Particularly, it relates to a flame-retardant resin composition which, in a molten state, scarcely deposits on metals, and is short in retainment time during working and molding operations, free from a qualitative defect such as yellowing and the like and improved in workability and moldability.
The flame-retardant compositions comprising a styrene based resin, a brominated bisphenol A epoxy resin and antimony trioxide are popularly used for interior and exterior parts of electric parts, business machines, etc., owing to their excellent light resistance.
Such a flame-retardant resin composition is proposed in JP-A-62-4737 (1987). More specifically, there is disclosed in the JP-A-62-4737 (1987) a flame-retardant resin composition comprising 100 parts by weight of a styrene based resin, 3 to 40 parts by weight of a flame-retardant obtained by heating a halogenated bisphenol A epoxy resin and a halogenated phenol such as tribromophenol, dibromocresol, trichlorophenol and dichlorocresol in the presence of a basic catalyst, and 2 to 10 parts by weight of antimony trioxide.
The expansion of the range of use of the flame-retardant resin compositions comprising a styrene based resin, a brominated bisphenol A epoxy resin and antimony trioxide has brought about various collateral problems. For instance, due to the characteristics of the epoxy group in the brominated bisphenol A epoxy resin as an essential component of the flame-retardant resin composition, this composition tends to adhere to the metal portions of an extruder, molding machine, etc., giving rise to the problem that the composition be retained in the extruder, molding machine, etc., during working and molding operations.
Specifically, the flame-retardant resin compositions containing a brominated bisphenol A epoxy resin in large quantities have many problems of sticking to screw(s) in the extruder or molding machine due to their high metal adhesive property in a molten state, thereby rising an inconstant discharge in the case of extruder, an inconstant measuring time in the case of molding machine, or an improper stripping of sheet in the case of heated rolls. Also, since the retainment (detention) time of the resin composition in the molding cylinder, hot-runner mold, etc., is elongated, there may take place decoloration (burning) or yellowing on the molded product.
In order to solve these problems, it is attempted in the art to add various kinds of wax, metallic soap, silicone oil or the like, but it needs to add a large quantities (such as 0.3 to 5 wt %) of the said substance for solving the above problems. Addition of a wax or metallic soap in large quantities, however, results in a marked reduction of flame retardant property, thermal stability and heat resistance, and an increased plate-out in the mold. Also, addition of silicone oil in large quantities aggrandizes wear of metal and makes the molding cylinder and screw susceptible to damage.
As a result of the present inventors' earnest studies for solving the above-mentioned defects, it has been found that by adding a specific methacrylate polymer at the specific amount to a composition of styrene based polymer containing a brominated bisphenol epoxy resin as a flame retardant and antimony trioxide, the thus obtained resin composition is low in adhesiveness to metals in a melten state and excellent in workability and moldability, while maintaining high flame retardant property, thermal stability and heat resistance with suppressed plate-out. The present invention has been attained on the basis of this finding.